So turns out the "flat cat 7 cable" I got about 10 years ago with a length of 15m for about 20 bucks was a scam. Was fine enough for lan but trying to push HDMI over it shows how much interferences it causes in itself (As about half of it's length is spooled).
Not really surprising but I didn't expect it to be that shitty either.
Probably the next "project" to change that one. Then I also can cut it open, as it was getting "heavy use" by passing through the door right next to the hinges… #CAT7
